1. Field of the Invention
The present invention relates to magneto-resistive thin film magnetic heads, and more particularly to a magneto-resistive thin film magnetic head employing a magneto-resistive element (hereinafter referred to as an MR element) so as to read digital information recorded on a magnetic recording medium as a magnetic field strength signal from the magnetic recording medium.
2. Description of the Related Art
Conventionally, a magneto-resistive thin film magnetic head (hereinafter referred to as an MR head) which employs an MR element and yokes to lead magnetic flux from a magnetic recording medium to the MR element.
FIGS. 1 through 3 each show a conventional yoke-type MR head. In the following description, the left and right sides of the MR head shown in FIGS. 1 through 3 are defined as front and rear sides of the MR head, respectively. Ag shown therein, the yoke-type MR head includes a nonmagnetic substrate 2 on which a lower yoke 11, an upper yoke 12, an MR element 21, and nonmagnetic insulating layers 31 and 32 are provided. The lower yoke 11 includes a front portion 11a, a rear portion 11b, and a center portion 11c. The upper yoke 12 includes a front portion 12a and a rear portion 12b. 
Each of the lower and upper yokes 11 and 12 is formed of a ferromagnetic material, and a gap 22 is formed between the front and rear portions 12a and 12b of the upper yoke 12. The upper yoke 12 is separated by the gap 22 into the front and rear portions 12a and 12b. 
The MR element 21 is provided below the position where the gap 22 is formed in the upper yoke 12 so as to be magnetically coupled to the front and rear portions 12a and 12b of the upper yoke 12. The lower yoke 11 and the rear portion 12b of the upper yoke 12 are Joined to be magnetically coupled. A reproducing head gap 15 (minute gap) is formed between the lower yoke 11 and the front portion 12a of the upper yoke 12.
According to this structure, the front portion 12a of Me upper yoke 12, the MR element 21, the rear portion 12b of the upper yoke 12, and the lower yoke 11 form a magnetic circuit in the yoke-type MR head so that magnetic flux of a signal from a magnetic recording medium such as a magnetic tape, which flux is detected by the reproducing head gap 15, is converted into au electric signal by the MR element 21 so as to obtain a reproduced output (signal). The nonmagnetic insulating layers 31 and 32 ore formed between the lower and upper yokes 11 and 12.
FIG. 4 shows the waveform of a reproduced signal which is obtained when a reproduction process is performed, using the yoke-type MR head having the above-mentioned structure, on a magnetic tape 1 on which bits having an equal recording wavelength are recorded (namely a magnetic tape on which recorded is a signal which Is reversed magnetically at a predetermined period).
As described above, the signal, which is reversed magnetically at the predetermined period, is recorded on the magnetic tape 1. Therefore, if the reproduction process is well performed, a rectangular signal shown by a dot-dash line in FIG. 4 should be output. However, as shown in FIG. 4, the conventional MR head distorts the waveform of the reproduced signal (output).
FIG. 3 is a diagram for illustrating the reason for the generation of the distortion of the waveform of the reproduced signal. As shown therein, a plurality of bits 3nxe2x88x921 through 3n+2 . . . Having the equal recording wavelength are formed on the magnetic tape 1. Further, magnetic reversal regions 4nxe2x88x921 through 4n+3 . . . are formed on corresponding boundary portions each formed between each adjacent two of the bits 3nxe2x88x921 through 3n+2 . . . A recent trend toward a high-density magnetic recording requires a shorter recording wavelength. As a result, each of the bits 3nxe2x88x921 through 3n+2 . . . is also required to have a shorter length in the running directions (indicated by arrows A1 and A2 in FIG. 3) of the magnetic tape 1.
According to FIG. 3, the reproducing head gap 15 formed in the MR head opposes the bit 3n. Magnetic flux 5 from the magnetic reversal region 4n, as indicated by an arrow in FIG. 3, forms a magnetic path from the front portion 12a of the upper yoke 12 to the magnetic reversal region 4n+1 by way of the MR element 21, the rear portion 12b of the upper yoke 12, and the lower yoke 11.
When the magnetic flux 5 passes through the MR element 21, the MR element 21 varies an electrical resistance in accordance with a magnetic field applied thereto. Therefore, by causing a sense current to flow through the MR element 21 in advance, a variation in the electrical resistance can be obtained as a value of a voltage drop. The reproduced signal can be thus obtained.
According to FIG. 3, if the length of the recording wavelength is equal to or more than the thickness of the front portion 12a of the upper yoke 12, magnetic flux (hereinafter referred to as unnecessary magnetic flux) 6 from the magnetic reversal region 4, toward the magnetic reversal region 4nxe2x88x921, which is in close proximity to the magnetic reversal region 4n, enters the MR element 21 through the front portion 12a of the upper yoke 12.
In other words, since a nonmagnetic coating layer of aluminum oxide (Al2O3) is provided on the front portion 12a of the upper yoke 12, the unnecessary magnetic flux 6 from the magnetic reversal region 4, goes to the front portion 12a of the upper yoke 12, which front portion has low magnetic reluctance. Although the direction of the unnecessary magnetic flux 6 is equal to that of the magnetic flux 5 from the proper magnetic reversal regions 4n and 4n+1, the unnecessary magnetic flux 6 interferes with the magnetic flux 5, thus causing the distortion of the waveform of the reproduced signal shown in FIG. 4.
It IS a general object of the present invention to provide a magneto-resistive thin film magnetic head in which the above disadvantage is eliminated. A more specific object of the present invention is to provide a magneto-resistive thin film magnetic head which is allowed to have an excellent reproduction characteristic by preventing unnecessary magnetic flux from entering a yoke so as to preclude the waveform of a reproduced signal from being distorted.
The above objects of the present invention are achieved by a magneto-resistive thin film magnetic head including: a base; a first yoke provided on the base and separated by a gap into first and second portions, the first portion including a side which opposes a magnetic recording medium; a magneto-resistive element which is magnetically coupled to the first and second portions of the first yoke and detects a magnetic recording signal; a second yoke formed on the first yoke so as to form a reproducing head gap between the first portion of the first yoke and the second yoke; and a third yoke provided between the first portion of the first yoke and the bass so as to be magnetically coupled to the first portion of the first yoke, wherein the reproducing head gap, the first portion of the first yoke, the magneto-resistive element, the second portion of the first yoke, and the second yoke form a circular magnetic circuit.
According to the above-described magneto-resistive thin film magnetic head, the third yoke is provided between the first portion of the first yoke and the base so as to be magnetically coupled to the first portion of the first yoke. Therefore, even if a length of each bit recorded on the magnetic recording medium becomes shorter as a result of a high-density recording, magnetic flux (unnecessary magnetic flux) from a bit in a position separate from a bit opposing the reproducing head gap flows into the third yoke and Is prevented from flowing into the magneto-resistive element via the first yoke because of the existence of the third yoke in a position opposing the magnetic recording medium between the first portion of the first yoke and the base. Similarly, in the case of a bit having a longer length, the unnecessary magnetic flux can be prevented from flowing into the magneto-resistive element by providing the third yoke. The third yoke gives a more remarkable effect in the case of a longer bit.
Therefore, only magnetic flux (proper magnetic flux) from the bit opposing the reproducing head gap flows through the first yoke. Thus, the unnecessary magnetic flux does not interfere with the proper magnetic flux, so that an excellent reproduced signal can be obtained.
The above objects of the present invention are also achieved by a magneto-resistive thin film magnetic head including: a base; a first yoke provided on said base and separated by a gap into first and second portions, the first portion including a side which opposes a magnetic recording medium; a magneto-resistive element which is magnetically coupled to the first and second portions of the first yoke and detects a magnetic recording signal; a second yoke formed on the first yoke so as to form a reproducing head gap between the first portion of the first yoke and the second yoke; and a third yoke which is provided on the second yoke so as to be magnetically coupled thereto, wherein the reproducing head gap, the first portion of the first yoke, the magneto-resistive element, the second portion of the first yoke, and the second yoke form a circular magnetic circuit.
According to the above-described magneto-resistive thin film magnetic head, the third yoke is provided on the second yoke so as to be magnetically coupled thereto. Therefore, even if a length of each bit recorded on the magnetic recording medium becomes shorter as a result of a high-density recording, magnetic flux (unnecessary magnetic flux) from a bit in a position separate from a bit opposing the reproducing head gap flows into the third yoke and is prevented from flowing into the magneto-resistive element via the second yoke because of the existence or the third yoke in a position opposing the magnetic recording medium on the second yoke. Similarly, in the case of a bit having a longer length, the unnecessary magnetic flux can be prevented from flowing into the magneto-resistive element by providing the third yoke. The third yoke gives a more remarkable effect in the case of a longer bit.
Therefore, only magnetic flux (proper magnetic lux) from the bit opposing the reproducing head gap flows through the second yoke. Thus, the unnecessary magnetic lux does not interfere with the proper magnetic flux, so that an excellent reproduced signal can be obtained.
The above objects of the present invention are further achieved by a magneto-resistive thin film magnetic head including: a base; a first yoke provided on the base; a second yoke which is formed on the first yoke and separated by a gap into first and second portions so as to form a reproducing head gap between the first portion and the first yoke, the first portion including a side which opposes a magnetic recording medium; a magneto-resistive element which is magnetically coupled to the first and second portions of the second yoke and detects a magnetic recording signal; and a third yoke Which is provided on the first portion of the second yoke so as to be magnetically coupled thereto, wherein the reproducing head gap, the first portion of the second yoke, the magneto-resistive element, the second portion of the second yoke, and the first yoke form a circular magnetic circuit.
According to the above-described magneto-resistive thin film magnetic head, the third yoke is provided on the first portion of the second yoke so as to be magnetically coupled thereto. Therefore, even if a length of each bit recorded on the magnetic recording medium becomes shorter as a result of a high-density recording, magnetic flux (unnecessary magnetic flux) from a bit in a position separate from a bit opposing the reproducing head gap flows into the third yoke and is prevented from flowing into the magneto-resistive element via the second yoke because of the existence of the third yoke in a position opposing the magnetic recording medium on the first portion of the second yoke. Similarly, in the case of a bit having a longer length, the unnecessary magnetic flux can be prevented from flowing into the magneto-resistive element by providing the third yoke. The third yoke gives a more remarkable effect in the case of a longer bit.
Therefore, only magnetic flux (proper magnetic flux) from the bit opposing the reproducing head gap flows through the second yoke. Thus, the unnecessary magnetic flux does not interfere with the proper magnetic flux, so that an excellent reproduced signal can be obtained.